1. Field of the Invention
This invention relates generally to optical communication systems. In particular, the invention pertains to error analysis of optical components in optical communication systems.
2. Description of the Background Art
Opto-electronic components, including fiber optics cables, connectors, transmitters, receivers, switches, routers and all other types of optical components, have become the backbone of the modern telecommunication infrastructure. Due to their extremely low error rate and wide bandwidth, optical communication systems have supported an explosion in the growth of data communication systems, such as the Internet. As the need for components in such systems increases, the need for accurate testing of these systems also increases.
Each component within an optical communication system must be tested to ensure that it meets technical standards that have been set in the industry. Additionally, the components must be tested to assess their performance in various real world conditions. This testing can be labor intensive, tedious and time consuming.
A known testing scheme 10 is shown in FIG. 1. The scheme 10 typically includes an optical transmitter 12, an optical attenuator 14, an optical monitor 16 and a receiver 18, such as an optical or electrical receiver. The device under test 25 (DUT) is placed between the transmitting side 20 (which comprises the transmitter 12, the attenuator 14 and the optical monitor 16) and the receiving side 22 (which comprises the receiver 18). All of these components are then interconnected with fiber optic cables and connectors.
In order to test the DUT 25, a technician energizes the optical transmitter 12 which transmits a test signal. The optical test signal is transmitted from the optical transmitter 12, through the optical attenuator 14, through the DUT 25 and is received by the receiver 18. The technician adjusts the gain of the optical attenuator 14 until the optical monitor 16 indicates that the output optical power is at a predetermined level for testing the DUT 25. The DUT 25 is tested at this predetermined optical power and the number of errors in the received signal is measured at the receiver 18. A bit error rate (BER) of the DUT 25 at the predetermined optical power is determined, in accordance with Equation 1:                     BER        =                              errors                          total              ⁢                                                           ⁢              number              ⁢                                                           ⁢              of              ⁢                                                           ⁢              bits              ⁢                                                           ⁢              received                                .                                    (        1        )            This value is compared to a specified BER for that specific power level, to determine whether the DUT 25 meets the industry standard.
There are drawbacks to this approach. Although the test results at the specified power level may be acceptable, the DUT 25 may perform unexpectedly poor at other power levels, in particular higher power levels. To illustrate, a DUT 25 may be expected to have a BER of 10−9 at the specified power level. However, at a much greater power level, a well behaved DUT 25 may be expected to have a BER of 10−16. Although the DUT 25 may test at the specified power level with a BER of 10−9, it may have a BER of 10−10 at the higher power level. As a result, the DUT 25 in real world conditions would have an unacceptable performance.
To evaluate the DUT 25 for such conditions, the DUT 25 may be tested at other optical power levels. Using the BERs at these optical power levels, the BER measurements of the DUT 25 are plotted on log paper, as shown in FIG. 2 for example. The optical power in decibel milliwatts (dBm) is plotted on the horizontal axis against the logarithm to the base 10 (log10) of the BER on the vertical axis.
However, constructing these plots can be extremely time consuming and tedious. Additionally, testing using these logarithmic plots typically requires an engineer to evaluate the plotted relationships. As shown in FIG. 2, all of plotted data does not fall on straight line 28. As a result, the engineer must analyze the raw data to determine whether the error rate versus power relationship is an indicator of poor performance of the DUT 25, or merely an acceptable statistical deviation from the norm. This testing procedure is labor intensive and is susceptible to human error. Accordingly, it is desirable to have alternate approaches for error analysis of optical components.